The present invention relates to a method of producing parcelling or packaging film for parcelling a freshness keeping agent and to a closed container or package within which is placed a package employing such parcelling film and freshness keeping agent together with a food, medicine or the like for the purpose of preserving freshness of such an object.
Hitherto, freshness keeping agents such as drying agents, antiseptics, insecticides, de-oxidizers and so forth have been used for the purpose of preventing deterioration, of the quality of a food, medicine or the like (such substances referred to generally as "object" hereinafter) attributable to the influence of moisture, oxygen or microorganisms so as to keep such an object fresh. These freshness keeping agents are sealed in a closed container together with the object. It has been often experienced that the freshness keeping agent is contaminated by oil or water of the food due to direct contact between the object and the freshness keeping agent, with the result that the function of the freshness keeping agent is impaired. Another problem is that the freshness keeping agent is mixed with the object so as to be eaten.
In order to avoid such inconveniences and problems, it has been a common practice to parcel the freshness keeping agent so as to isolate it from the object within the closed container. Practically, a separation film is provided on a portion of the container such that the object and the freshness keeping agent are disposed on opposite sides of the film so as to be isolated from each other.
For instance, Japanese Utility Model Unexamined Publication No. 50-130554 discloses a container for preventing degradation of the content in which an oxygen absorber parcel is attached to an inner surface of a container such as a bottle, can or the like so as to face the interior of the container, the oxygen absorber parcel consisting of a chemical agent which produces carbon dioxide upon absorption of oxygen parcelled in a gas-permeable plastic material such as a low-density polyethylene film. The gas-permeable material isolating the chemical agent and the content, which is made from a plastic film such as polyethylene film, exhibits a large resistance to the permeation of the oxygen or carbon dioxide gas, so that the parcel could not function effectively when used for the purpose of maintaining the freshness of an object such as food which tends to be degraded quickly.
Japanese Utility Model Unexamined Publication No. 54-44253 discloses a formed closed container in which a pocket is provided on an inner lid formed on a stepped portion of the formed closed container and a quality preserving agent is placed in the pocket. In this container, the inner lid is merely placed on a step of the container so that there is a risk of the contents entering the compartment of the quality preserving agent in the event the container is dropped, particularly when the contents is a powder or a liquid. Thus, this container cannot isolate the agent and object.
Furthermore, Japanese Utility Model Unexamined Publication No. 55-80261 discloses a cap for closing the mouth of a container, the cap being provided at the side facing the interior of the container with a deoxidizing agent by means of an oxygen permeable material having minute pores and capable of preventing permeation of liquids therethrough. The oxygen-permeable material used in this art is produced by cold orientation of a film made of polypropylene, polyethylene fluoride or the like.
This film material, however, has inferior formability, although it exhibits excellent gas-permeability while preventing permeation of liquids. The term "formability" is used in this specification to mean an enabling nature of a material to be formed into a specific stable form. Namely, this film material tends to exhibit thermal contraction and cracking at corners even when the forming is effected in a vacuum atmosphere, so that it cannot constitute a de-oxidizing agent parcel having a high degree of practicalness. The forming of this film has to be effected such that the oxygen permeable material has a small thickness and the de-oxidizing agent housing portion has to be made by making use of elongation of the material. Thus, the film material used in this art is still unsatisfactory in the aspects of producibility and strength. In addition, the oxygen permeable materials used in this art generally have poor resistance to oil and alcohol, so that the film material tend to allow permeation of oil or alcohol when the contents or object to be preserved contains oil or alcohol, with the result that the gas-permeability is impaired with deterioration the performance of the de-oxidizing agent.
In order to overcome these problems, Japanese Patent Unexamined Publication No. 58-64959 discloses an art in which a parcelling material made of a porous film or a non-woven cloth is impregnated or coated with a fluororesin. Such porous film or non-woven cloth is hydrophobic so that the fluororesin with which the film or cloth is impregnated or coated cannot sufficiently penetrate into the entire portion of the film material or fibrous structure of the cloth. Namely, the fluororesin is present only on the surface region of the parcelling material. Thus, the parcelling material used in this art cannot provide sufficient resistance to oil and alcohol. The porous film or the non-woven cloth has local portions having large pores so that oil or alcohol tends to reach the de-oxidizing agent in the parcel through such large pores, despite the presence of fluororesin with which the parcelling material is impregnated or coated. It has proved also that the de-oxidizing agent parcel formed from this parcelling material faces the same problem as that encountered with the art of Japanese Utility Model Unexamined Publication No. 55-80261, i.e., inferior producibility and material strength.
Thus, all the known parcelling materials for parcelling freshness keeping agent require improvement in the aspects of gas-permeability, strength, simplicity of construction and producibility.